One in eight. That’s how many new cancer cases worldwide in 2024 were caused by an infection, according to a major new analysis from the World Health Organization’s cancer agency. That adds up to roughly 2.3 million diagnoses, and most of them came from just five germs, several of which you can vaccinate against, test for, or cure.
The study, from the International Agency for Research on Cancer (IARC), is the most complete look yet at infections that cause cancer. The headline message from the researchers is blunt: this is a huge burden, and much of it is preventable. Here’s what the study found, how the U.S. compares, and the four practical steps worth bringing up at your next checkup.
What the New IARC Study Found
The paper, “Global burden of cancer attributable to infections in 2024: a worldwide incidence analysis,” was published September 28, 2026, in The Lancet Oncology. It was led by IARC epidemiologist Dr. Harriet Rumgay and drew on cancer estimates from IARC’s Global Cancer Observatory.
The researchers counted cancers caused by 12 infectious agents known to cause cancer in humans: viruses, one bacterium and several parasites. According to IARC’s official press release, about 2.3 million new cancer cases in 2024, or about 12% of all new cases, were caused by those infections.
“Despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on populations in low- and middle-income countries,” Rumgay said in the release.
Speaking to Healio, she put it more simply: “While this burden is enormous, it is also largely preventable.”
The 5 Infections That Cause Cancer Most Often
Twelve germs were studied, but five did almost all the damage. Here are IARC’s estimates for 2024:
| Infection | Estimated new cancer cases (2024) | Main cancers linked |
|---|---|---|
| H. pylori (bacterium) | ~760,000 | Stomach (gastric) cancer |
| HPV (human papillomavirus) | ~750,000 | Cervical, throat, anal and other cancers |
| Hepatitis B (HBV) | ~360,000 | Liver cancer |
| Epstein-Barr virus (EBV) | ~260,000 | Nasopharyngeal cancer, lymphomas, some stomach cancers |
| Hepatitis C (HCV) | ~160,000 | Liver cancer |
The other seven agents on the list were HIV, Kaposi sarcoma-associated herpesvirus (KSHV), HTLV-1, Merkel cell polyomavirus, and three parasites: Schistosoma haematobium and the liver flukes Opisthorchis viverrini and Clonorchis sinensis.
The surprise: Epstein-Barr virus
EBV, the virus behind mono, now ranks fourth, ahead of hepatitis C. That’s partly because newer evidence ties it to some stomach cancers, not just the nasopharyngeal cancer and lymphomas it was already known for. Rumgay told Healio this was one of the “most striking” findings.
There’s a catch: unlike HPV and hepatitis B, there is no vaccine for EBV yet. Senior author Dr. Gary Clifford said the analysis highlights where new prevention tools “could have the greatest impact, particularly for infections such as EBV, for which effective vaccines are not yet available.”
Where Infection-Related Cancers Hit Hardest
The burden is wildly uneven. Eastern Asia alone accounted for 42% of all infection-related cancers worldwide, about 990,000 cases, driven largely by H. pylori and hepatitis B. In that region, roughly 15% of all new cancers were linked to infections, Healio reported from the paper.
Sub-Saharan Africa had the highest share: about 25% of new cancers there were tied to infections, driven by HPV and KSHV and made worse by HIV. Overall, more than three-quarters (77%) of infection-related cancers occurred in low- and middle-income countries.
What about the U.S.?
North America is near the bottom of the list. About 5% of new cancers in the region were attributable to infections, according to the study figures reported by Healio, one of the lowest shares in the world, alongside Western Europe and Oceania.
Low doesn’t mean zero, though. The CDC estimates HPV alone causes about 39,300 cancers in the U.S. each year. And liver and stomach cancers linked to hepatitis and H. pylori still affect thousands of Americans, often people who never knew they were infected.
How Infections That Cause Cancer Do Their Damage
First, a reassurance: cancer itself isn’t catching. What spreads is the germ, and in a small share of people a long-term infection slowly sets the stage for cancer over years or decades.
In a piece for The Conversation, researchers John La Marca and Sarah Diepstraten explained the main routes. Some viruses switch off a cell’s built-in brakes on growth. Others insert their own DNA into ours, disrupting genes that control cell division. Bacteria like H. pylori and parasites work more indirectly, causing chronic inflammation that damages tissue and leads to DNA errors as the body keeps repairing itself.
The key point: most people infected with these germs never get cancer. Infection raises the risk, and other factors (your immune system, smoking, alcohol, genetics) shape what happens next. That long, slow timeline is exactly why infections that cause cancer are such a good prevention target: it gives vaccines, testing and early treatment room to work.
Preventing Infections That Cause Cancer: 4 Steps for Americans
IARC says most infection-related cancers “can already be prevented through well-established public health measures.” Here’s how that translates into U.S. guidance.
1. Get the HPV vaccine on schedule (or catch up)
The CDC recommends two doses of HPV vaccine at ages 11 to 12, and it can start as early as age 9. Catch-up vaccination is recommended for everyone through age 26. Adults 27 to 45 who weren’t fully vaccinated can decide with their clinician, though the benefit is smaller because many have already been exposed. Regular cervical cancer screening still matters, vaccinated or not.
2. Make sure you’re protected against hepatitis B
Under ACIP recommendations adopted in 2022, all U.S. adults ages 19 to 59 should get the hepatitis B vaccine, and older adults with risk factors should too. For newborns, federal guidance changed after a December 2025 ACIP vote: the CDC now recommends individual decision-making on the birth dose for babies whose mothers test negative, while the American Academy of Pediatrics still recommends a universal birth dose. If you’re unsure of your own status, a simple blood test can tell you.
3. Get tested for hepatitis C at least once
The CDC recommends hepatitis C screening for every adult 18 and older at least once in their lifetime, plus during each pregnancy and more often for people with ongoing risk. This one has a big upside: modern oral medicines taken for 8 to 12 weeks cure more than 95% of people, according to the CDC. Curing the infection removes it as an ongoing driver of liver damage.
4. Ask about H. pylori testing if you’re at higher risk
There’s no routine U.S. screening for H. pylori. But the American College of Gastroenterology’s 2024 guideline recommends testing people at increased risk of stomach cancer, including anyone with a parent, sibling or child who had stomach cancer, and testing household members of someone who tests positive. If you have it, it’s treatable with antibiotics, followed by a test to confirm it’s gone.
Bonus: HIV prevention and care
HIV raises the risk of several infection-related cancers by weakening the immune system. Testing, treatment and prevention tools like PrEP all lower that risk. Again, a conversation with your doctor is the place to start.
What This Study Can and Can’t Tell You
This is a modeling study, not a trial. The researchers combined cancer estimates with data on how often each infection is involved in each cancer type to calculate how many cases are “attributable” to infections. Those are best estimates, and the data quality varies a lot by country.
It’s also not a trend report. The proportion caused by infections looks lower than past IARC estimates (18% in 2002, for example), but the authors caution the numbers can’t be compared reliably because the data sources have changed. And the regional figures above come from news coverage of the paper rather than the full text, which sits behind a paywall.
Finally, “attributable” doesn’t mean an infection was the only cause. A smoker with hepatitis B, for instance, has more than one thing pushing toward liver cancer.
Related Reading on Cancer Prevention
If you’re thinking about cancer screening more broadly, check out our look at new research on mammogram overdiagnosis. We also covered a study linking GLP-1 drugs to lower breast cancer risk. And parents weighing shots this season can see our fall 2026 kids’ vaccine guide.
The Bottom Line: Your Infection-Cancer Checklist
Infections that cause cancer are responsible for about 2.3 million cases a year worldwide, and the U.S. is among the luckier regions. But many Americans still carry hepatitis B, hepatitis C, HPV or H. pylori without knowing it. Before your next appointment, run through this list:
- HPV: Are you (and your kids) vaccinated? Up to date on cervical screening?
- Hepatitis B: Have you ever been vaccinated or tested?
- Hepatitis C: Have you had your once-in-a-lifetime screening test?
- H. pylori: Does stomach cancer run in your family, or has someone in your home tested positive?
None of these steps requires anything dramatic, just a question at your next visit. This article is for general information and isn’t medical advice, so talk to your doctor about which tests and vaccines make sense for you.
